Improve w2_wages_from_qualified_business imputation

[MaxGhenis]

Currently we're setting it to 10.1% of qualified business income sources (not considering deductions):

policyengine-us-data/policyengine_us_data/datasets/puf/puf.py

Lines 209 to 210 in 92d51e9

	W2_WAGES_SCALE = 0.101
	puf["w2_wages_from_qualified_business"] = qbi * W2_WAGES_SCALE

Let's add some stochasticity at a minimum. It also doesn't make a lot of sense to tie W2 wages to QBI, given W2 wages subtract from QBI which is a net concept.